(a) Field of the Invention
The present invention relates to a method and an apparatus for fingerprint recognition.
(b) Description of the Related Art
A biometric recognition technology using fingerprint information has been researched for a long period of time and various methods are known. A fingerprint refers to a shape created based on a line in which a sweat gland of a skin at the tip of the finger is raised, that is, a ridge. A depressed part between ridges is referred to as a valley. Overall, the ridge may be formed along a constant path and may be divided into a bow pattern, a swirl pattern, a horseshoe pattern, and the like. The shape of the fingerprint is different for every person, and it has been actively researched as a unique biometric recognition means until recently.
As basic feature information for the fingerprint recognition, two points based on local features of the ridge pattern are considered. These two points are an ending point where the ridge is interrupted and a bifurcation point where the line is branched. In detail, general feature information for the fingerprint recognition are expressed by coordinate values x and y on the fingerprint image of the points, an angle θ of the ridge of each point, and a characteristic bit information value b representing whether the point is the bifurcation point or the ending point. These contents are already widely known to international standards such as ISO/IEC 19794.
Basically, biometric information is influenced by many environmental variables, so the same biological image may not be acquired every time. In the case of the fingerprints, different fingerprint images may be obtained each time because of non-uniform pressure from a user, rotation deformation, and foreign material insertion, such as sweat or dust, when using a fingerprint authentication system. As a result, a geometric deformation occurs in the extracted feature information, thereby making it difficult to achieve an adequate recognition rate.
In order to design a fingerprint recognition system that is strong to the geometric deformation of the fingerprint image, a method to utilize the number of ridges has been researched. The ridges may exist and the number of ridges may be defined between arbitrary feature points in one fingerprint image. The number of ridges does not change even if the valley interval changes on the fingerprint image by the external pressure, and the number of ridges between two feature points does not change when the rotated image is scanned. In this way, the number information of the ridges may be used as invariant feature information even if the geometric deformation of the image occurs. As a patent for the fingerprint recognition system using the number of ridges, there are U.S. Pat. Nos. 4,944,021, 6,266,433, and Korean publication No. 10-2004-0078290, etc.
Since the number of ridges is calculated based on a certain feature point, the deformation for the flow of the ridges or the inserting, the deletion, the movement, or the like of the feature points must be considered in the fingerprint recognition using the number information of the ridges. The conventional methods only use the ridge number information between specific feature points according to reference points, a certain range, or a constant rule for the fingerprint recognition. As a result, the conventional methods are vulnerable to insertion, deletion, movement, or the like of the feature points. For example, U.S. Pat. No. 4,944,021 proposes a method of defining ridge number values between reference feature points and feature points existing in each quadrant as one group, and searching for a group that is similar to the group. However, there is a problem that a match is impossible when the direction of the reference feature points is rotated or the reference feature points are not displayed when scanning the fingerprint image.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.